This invention concerns means and methods for semiconductor devices and, more particularly, improved means and methods for semiconductor devices having buried doped layers covered by an epitaxial layer.
It is common in the semiconductor art to form semiconductor devices in which doped regions are buried within the semiconductor material underneath an epitaxial semiconductor layer. An example of such a region commonly used in bipolar integrated circuits is a buried collector contact referred to in the art as a "buried layer". As used herein, the words "buried layer" or "buried region" or "buried layer region" are intended to refer not only to buried bipolar transistor collector contacts, but generally to doped regions having relatively higher doping buried beneath epitaxial layers in semiconductor devices.
There are many circumstances wherein it is desired to form buried layers which are more highly doped than the overlying material. However, when epitaxial layers are formed above highly doped buried layers it is found that the defect density in the epi-layer is generally much higher above the buried layers than elsewhere. The presence of the relatively high doping density in the buried layers produces a variety of surface defects which adversely influence the perfection of the epi-layer grown thereon. This is undesirable since defects in the epi-layer, particularly in active regions such as are commonly found above buried layers, are a source of low yield during semiconductor device manufacture.
Despite the fact that buried layers of boron, antimony, arsenic, phosphorous and other dopants are widely used in semiconductor devices, the problem of epi defects related to buried layers has not been entirely solved. Thus, a need continues to exist for improved means and methods for reducing the defect densities in epitaxial layers formed over buried layers.
Accordingly, it is an object of the present invention to provide improved means and methods for forming epitaxial layers on semiconductor substrates containing buried layers or other buried regions of higher doping than the overlying epi-layer.
It is an additional object of the present invention to provide improved means and methods for forming epitaxial layers on semiconductor substrates containing arsenic doped buried layers.
It is a further object of the present invention to provide improved means and methods for forming epitaxial layers on semiconductor substrates containing both arsenic doped buried layers and buried layers having other dopants.
It is an additional object of the present invention to provide improved means and methods for forming epitaxial layers on semiconductor substrates containing arsenic doped buried layers by minimizing arsenic precipitation prior to epitaxial layer growth.